Current-mode analog baseband apparatus

ABSTRACT

A current-mode analog baseband apparatus is provided. The apparatus includes a current-mode low-order filter, a current-mode programmable gain amplifier (PGA) unit and a high-order filter. The input impedance is smaller than the output impedance in the current-mode low-order filter. An input terminal of the current-mode PGA unit is connected to an output terminal of the current-mode low-order filter. An input terminal of the high-order filter is connected to an output terminal of the current-mode PGA unit.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 99123835, filed on Jul. 20, 2010. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of specification.

BACKGROUND

1. Field of the Disclosure

The disclosure relates to a communication system. More particularly, thedisclosure relates to a current-mode analog baseband apparatus.

2. Description of Related Art

In an ultra-wide band (UWB) wireless communication system, signal datais transmitted by orthogonal frequency division multiplexing (OFDM). Todecode the signal data at a transceiver end, an analog basebandapparatus demultiplies the signal from radio frequency (RF) to baseband(0-250 MHz), and an analog to digital converter (ADC) is used to converta baseband signal into a digital signal. During the above operations, again of the baseband must be consistent. However, in a present circuitdesign, a voltage-mode amplifier and a voltage-mode filter cannot beoperated over 100 MHz. In a receiver of the UWB system, since thecircuit is usually operated in a non-linear zone due to interferencesignals during a process of demultiplying the signal from the RF to thebaseband, it is important to consider linearity. Moreover, withdevelopment of the semiconductor fabrication process, a circuitoperation voltage becomes lower. Therefore, it is practical andnecessary to design an analog baseband apparatus having features ofrejecting interference signals, high linearity, and low operationvoltage.

In a conventional intermediate frequency (IF) down-conversion design,design difficulties and power consumptions of a variable-gain amplifierand the voltage-mode filter are increased as bandwidths thereof areincreased. Although the IF down-conversion can resolve a problem ofdirect current (DC) offset, other problems are encountered, for example,linearity and power consumption. Therefore, a direction-converter isstill widely used in the UWB system. Anyway, in the present UWB system,the voltage-mode amplifier is used to implement the variable-gainamplifier. An input impedance of the voltage-mode amplifier is thegreater the better (which preferably approaches infinity), and an outputimpedance thereof is the smaller the better (which preferably approaches0). Contrary to the voltage-mode amplifier, an input impedance of acurrent-mode amplifier is the smaller the better (which preferablyapproaches 0), and an output impedance thereof is the greater the better(which preferably approaches infinity). In the present UWB system, thecurrent-mode amplifier is not yet used to implement the variable-gainamplifier.

SUMMARY

The disclosure is directed to an analog baseband apparatus, in which acurrent-mode structure is used to implement an analog baseband circuit.

The disclosure provides an analog baseband apparatus including acurrent-mode low-order filter, a first current-mode programmable gainamplifier (PGA) unit and a high-order filter. An input impedance issmaller than an output impedance in the current-mode low-order filter.An input terminal of the first current-mode PGA unit is connected to anoutput terminal of the current-mode low-order filter. An input terminalof the high-order filter is connected to an output terminal of the firstcurrent-mode PGA unit.

According to the above descriptions, regarding a broadband system, thesmaller a load resistance is, the wider an operation bandwidth is, andthe smaller the load resistance is, the better effect the currenttransmission is. Therefore, the current-mode low-order filter and thecurrent-mode PGA unit are used to implement the analog baseband circuit,which may have characteristics of broadband and high linearity.

In order to make the aforementioned and other features and advantages ofthe disclosure comprehensible, several exemplary embodiments accompaniedwith figures are described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the disclosure, and are incorporated in and constitutea part of this specification. The drawings illustrate embodiments of thedisclosure and, together with the description, serve to explain theprinciples of the disclosure.

FIG. 1 is a functional block schematic diagram of an analog basebandapparatus according to an exemplary embodiment of the disclosure.

FIG. 2 is a diagram illustrating an implementation of a high-orderfilter of FIG. 1.

FIG. 3A is a diagram illustrating an implementation of a current-modelow-order filter of FIG. 1.

FIG. 3B is a diagram illustrating an implementation of a current-modeamplifier of FIG. 3A.

FIG. 4 is a diagram illustrating another implementation of acurrent-mode low-order filter of FIG. 1.

FIG. 5 is a diagram illustrating an implementation of a firstcurrent-mode PGA unit of FIG. 1.

FIG. 6 is a circuit schematic diagram of a current-mode amplifier ofFIG. 5 according to an exemplary embodiment of the disclosure.

FIG. 7 is a functional block schematic diagram of an analog basebandapparatus according to another exemplary embodiment of the disclosure.

FIG. 8 is a diagram illustrating a simulation result of input impedanceof an analog baseband apparatus of FIG. 7.

FIG. 9 is a gain frequency response diagram of a current-mode PGA in ananalog baseband apparatus of FIG. 7.

FIG. 10 is a diagram illustrating a frequency response simulation resultof a current-mode low-order filter in an analog baseband apparatus ofFIG. 7.

FIG. 11 is a diagram illustrating a whole frequency response simulationand measurement result of an analog baseband apparatus of FIG. 7.

FIG. 12 is a diagram illustrating a whole noise characteristicmeasurement result of an analog baseband apparatus of FIG. 7.

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

A present complementary metal-oxide semiconductor (CMOS) amplifier has ahigh voltage gain. Regarding the amplifier with a fixed currentconsumption, a multiplication of a gain G and a bandwidth W thereof is aconstant C (i.e. G×W=C). Therefore, to obtain a relatively highbandwidth W and relatively high gain G, power consumption has to beincreased. However, a baseband requirement of ultra-wide band (UWB)cannot be reached regardless of how greater the power consumption is, sothat a method of adding a zero pole to the amplifier is used to increasethe multiplication of the gain and the bandwidth. However, when thebandwidth becomes greater (greater than 250 MHz), such method isinapplicable.

Most of the present analog baseband apparatus are constructed based on acircuit principle of V=I×R, and apply a voltage signal transmission modewithout using a current signal transmission mode. In the present analogbaseband apparatus, a current-mode amplifier is not yet used toimplement a variable-gain amplifier and a filter.

Regarding a broadband system, the smaller a load resistance is, thewider an operation bandwidth is, and the smaller the load resistance is,the better effect the current transmission is. Therefore, in thefollowing exemplary embodiments, a current-mode circuit structure isused to implement the UWB analog baseband apparatus. The analog basebandapparatus using the current-mode amplifier has characteristics ofbroadband and high linearity. Since an applicable bandwidth of thecurrent-mode amplifier can be more than 1 GHz, the analog basebandapparatus can be very competitive in a future ultra-wide bandapplication.

FIG. 1 is a functional block schematic diagram of an analog basebandapparatus 100 according to an exemplary embodiment of the disclosure.The analog baseband apparatus 100 includes a current-mode low-orderfilter 110, a first current-mode programmable gain amplifier (PGA) unit120 and a high-order filter 130. An input terminal of the current-modelow-order filter 110 receives a current-mode radio frequency (RF) signalI_(in). An input impedance of the current-mode low-order filter 110 issmaller than an output impedance thereof. The input impedance of thecurrent-mode low-order filter 110 is the smaller the better (whichpreferably approaches 0), and the output impedance thereof is thegreater the better (which preferably approaches infinity).

An input terminal of the first current-mode PGA unit 120 is connected toan output terminal of the current-mode low-order filter 110, and is usedfor receiving an output signal I₁ of the current-mode low-order filter110. An input impedance of the first current-mode PGA unit 120 issmaller than an output impedance thereof. The input impedance of thefirst current-mode PGA unit 120 is the smaller the better (whichpreferably approaches 0), and the output impedance thereof is thegreater the better (which preferably approaches infinity).

An input terminal of the high-order filter 130 is connected to an outputterminal of the first current-mode PGA unit 120, and is used forreceiving an output signal I₂ of the first current-mode PGA unit 120.According to different implementations of the high-order filter 130, anoutput signal I₃ can be a voltage-mode signal or a current-mode signal.The high-order filter 130 can be a current-mode filter or a voltage-modefilter of any type. For example, the high-order filter 130 can be awell-known gm-C low-pass filter.

FIG. 2 is a diagram illustrating an implementation of the high-orderfilter 130 of FIG. 1. The high-order filter 130 may include acurrent-to-voltage converter 210, a gm-C low-pass filter 220 and avoltage-to-current converter 230. A current input terminal of thecurrent-to-voltage converter 210 is connected to the output terminal ofthe first current-mode PGA unit 120 for receiving the current-modeoutput signal I₂. An input terminal of the gm-C low-pass filter 220 isconnected to a voltage output terminal of the current-to-voltageconverter 210 for receiving a voltage-mode output signal. The gm-Clow-pass filter 220 may perform a high-order (for example, 6-order)filtering. A voltage input terminal of the voltage-to-current converter230 is connected to the output terminal of the gm-C low-pass filter 220for receiving a voltage-mode filtering result. A current output terminalof the voltage-to-current converter 230 is connected to the outputterminal of the high-order filter 130 for providing the current-modeoutput signal I₃.

The high-order filter 130 can be a current-mode filter using currentconveyors. For example, the current conveyors can be used to form anintegrator, and the integrator is used to form the high-ordercurrent-mode filter. Such current-mode filter is a well-known technique,so that a detailed description thereof is not repeated herein. Anarticle authored by C. M. Chang, entitled “Multifunction biquadraticfilters using current conveyors” (IEEE Transactions on Circuits andSystems-II: Analog and Digital Signal Processing, 44, 956-958, 1997), oran article authored by Svoboda, J. A., entitled “Comparison of RCOP-Amp. And RC current conveyor filter” (Int. J. ELECTION., 76 (4), pp.615-626, 1994), or an article authored by SOLIMAN A. M, entitled“Current conveyor filters: classification and review” (Microelectron.J., 29, pp. 133-149, 1998), etc. may all be used as references toimplement the high-order filter 130 of FIG. 1. The above documents areentirely incorporated by reference herein.

The current-mode low-order filter 110 of FIG. 1 can be a current-modelow-pass filter of any type, for example, a current-mode Sallen Key (SK)low-pass filter, etc. FIG. 3A is a diagram illustrating animplementation of the current-mode low-order filter 110 of FIG. 1. InFIG. 3A, the circuit of the current-mode low-order filter 110 has asingle-ended structure. The current-mode low-order filter 110 includes acurrent-mode amplifier 310, an output capacitor C₁, a feedback capacitorC₂, a first resistor R₁ and a second resistor R₂. The current-modeamplifier 310 can be a current-mode amplifier of any type. Ideally, aninput terminal of the current-mode amplifier 310 can be equivalent to aninput impedance r_(i), and an output terminal thereof can be equivalentto a current source 311. If a current flowing through the inputimpedance r_(i) is i₁, a current of the current source 311 is F timesgreater than the current i₁ (i.e. F×i₁). The input impedance r_(i) ofthe current-mode amplifier 310 is smaller than an output impedancethereof (an impedance of the current source 311). The input impedancer_(i) of the current-mode amplifier 310 is the smaller the better (whichpreferably approaches 0). The smaller the input impedance r_(i) is, thebetter effect the current transmission of the RF signal I_(in) is, andthe smaller the input impedance r_(i) is, the wider an operationbandwidth is.

The input terminal of the current-mode amplifier 310 serves as the inputterminal of the current-mode low-order filter 110 for receiving the RFsignal I_(in). A first end of the feedback capacitor C₂ is connected tothe input terminal of the current-mode amplifier 310. A first end of theoutput capacitor C₁ and a first end of the first resistor R₁ are allconnected to the output terminal of the current-mode amplifier 310. Asecond end of the first resistor R₁ and a first end of the secondresistor R₂ are all connected to a second end of the feedback capacitorC₂. A second end of the second resistor R₂ serves as the output terminalof the current-mode low-order filter 110.

FIG. 3B is a diagram illustrating an implementation of the current-modeamplifier 310 of FIG. 3A. Referring to FIG. 3B, the current-modeamplifier 310 includes a current source 312, a current source 313, avoltage-mode amplifier 314, a voltage-mode amplifier 315, andtransistors T1-T10, wherein the transistors T1, T4, T7, T8 and T10 areP-channel metal oxide semiconductor (PMOS) transistors, and the othertransistors are N-channel metal oxide semiconductor (NMOS) transistors.A first end of the current source 312 is connected to a drain of thetransistor T9, and a second end of the current source 312 is connectedto a power voltage VDD. A gate of the transistor T9 is connected to thedrain of the transistor T9, and a source of the transistor T9 isconnected to a source of the transistor T10. A gate of the transistorT10 is connected to a drain of the transistor T10. A first end of thecurrent source 313 is connected to the drain of the transistor T10, anda second end of the current source 313 is connected to a ground voltage.

Sources of the transistors T1 and T2 are connected to the input terminalof the current-mode amplifier 310 for receiving the RF signal A gate ofthe transistor T2 is connected to the gate of the transistor 19. A drainof the transistor T7 is connected to a drain of the transistor T2. Asource of the transistor T7 is connected to the power voltage VDD. Anoutput terminal of the voltage-mode amplifier 314 is connected to gatesof the transistors T7 and T8. A non-inverted input terminal of thevoltage-mode amplifier 314 is connected to the drain of the transistorT2, and an inverted input terminal of the voltage-mode amplifier 314 isconnected to a source of the transistor T4.

A gate of the transistor T1 is connected to the gate of the transistorT10. A drain of the transistor T5 is connected to a drain of thetransistor T1, and a source of the transistor T5 is coupled to theground voltage. An output terminal of the voltage-mode amplifier 315 isconnected to gates of the transistors T5 and T6. A non-inverted inputterminal of the voltage-mode amplifier 315 is connected to the drain ofthe transistor T1, and an inverted input terminal of the voltage-modeamplifier 315 is connected to a source of the transistor T3.

A gate of the transistor T6 is connected to the gate of the transistorT5, a source of the transistor T6 is connected to the ground voltage,and a drain of the transistor T6 is connected to the source of thetransistor T3. A gate of the transistor T3 receives a bias voltageV_(b2). The gate of the transistor T8 is connected to the gate of thetransistor T7. A source of the transistor T8 is connected to the powervoltage VDD, and a drain of the transistor T8 is connected to the sourceof the transistor T4. A gate of the transistor T4 receives a biasvoltage V_(b1). Drains of the transistor T3 and T4 are connected to theoutput terminal of the current-mode amplifier 310 for providing acurrent i_(o).

FIG. 4 is a diagram illustrating another implementation of thecurrent-mode low-order filter 110 of FIG. 1. In FIG. 4, the circuit ofthe current-mode low-order filter 110 has a double-ended (a differentialpair) structure. In the present exemplary embodiment, the RF signalI_(in) of FIG. 1 includes a first RF signal I_(in+) and a second RFsignal I¹⁻, and the output signal I₁ includes a first output signal I₁₊and a second output signal I¹⁻.

The current-mode low-order filter 110 includes a current-mode amplifier400, a first output capacitor C₁, a second output capacitor C₃, a firstfeedback capacitor C₂, a second feedback capacitor C₄, a first resistorR₁, a second resistor R₂, a third resistor R₃ and a fourth resistor R₄.A first input terminal and a second input terminal of the current-modeamplifier 400 serve as the input terminal of the current-mode low-orderfilter 110 for respectively receiving the current-mode RF signalsI_(in +) and I_(in−). A first end of the first feedback capacitor C₂ anda first end of the second feedback capacitor C₄ are respectivelyconnected to the first input terminal and the second input terminal ofthe current-mode amplifier 400. A first end of the first outputcapacitor C₁ and a first end of the second output capacitor C₃ arerespectively connected to a first output terminal and a second outputterminal of the current-mode amplifier 400. A first end of the firstresistor R₁ and a first end of the third resistor R₃ are respectivelyconnected to the first output terminal of the current-mode amplifier400. A second end of the first resistor R₁ and a second end of the thirdresistor R₃ are respectively connected to a second end of the firstfeedback capacitor C₂ and a second end of the second feedback capacitorC₄. A first end of the second resistor R₂ and a first end of the fourthresistor R₄ are respectively connected to the second end of the firstresistor R₁ and the second end of the third resistor R₃. A second end ofthe second resistor R₂ and a second end of the fourth resistor R₄respectively serve as the output terminal of the current-mode low-orderfilter 110 for respectively providing the output signals I₁₊ and I¹⁻ tothe first current-mode PGA unit 120.

The current-mode amplifier 400 includes a feedback circuit 410, an inputstage 420 and an output stage 430. A first input terminal and a secondinput terminal of the input stage 420 respectively serve as the firstinput terminal and the second input terminal of the current-modeamplifier 400 for receiving the input currents I_(in+) and I_(in−). Theinput stage 420 generates corresponding inner currents I_(inner+) andI_(inner−) according to the input currents I_(in+) and feedback currentsI_(fb+) and I_(fb−) of the feedback circuit 410. The input stage 420 mayuse a common gate or common source complementary metal-oxidesemiconductor (CMOS) amplifier in collaboration with the feedbackcircuit 410 to achieve an effect of reducing the input impedance. Inother exemplary embodiments, the input stage 420 may use a common basebipolar junction transistor (BJT) amplifier in collaboration with thefeedback circuit 410 to achieve the effect of reducing the inputimpedance.

The feedback circuit 410 is connected to the input stage 420. Thefeedback circuit 410 generates the corresponding feedback currentsI_(fb+) and I_(fb−) according to the inner currents I_(inner+) andI_(inner−) of the input stage 420. In some exemplary embodiments, thefeedback circuit 410 can be a trans-impedance amplifier (TIA). Arelationship of the inner currents I_(inner+) and I_(inner−), the inputcurrents I_(in−), and the feedback currents I_(fb+) and I_(fb−) isdetermined according to a design requirement. For example, the innercurrent I_(inner+) is a sum of the input current I_(in+) and thefeedback current I_(fb+), and the inner current I_(inner−) is a sum ofthe input current I_(in−) and the feedback current I_(fb−). The feedbackcircuit 410 may reduce the input impedance of the input stage 420, so asto achieve a purpose of broadband.

A first input terminal and a second input terminal of the output stage430 are connected to a first output terminal and a second outputterminal of the input stage 420. The output stage 430 may mirror theinner currents I_(inner+) and I_(inner−) of the input stage 420 tointernal of the output stage 430. A first output terminal and a secondoutput terminal of the output stage 430 respectively serve as the firstoutput terminal and the second output terminal of the current-modeamplifier 400.

In FIG. 4, the input stage 420 includes a current source 421, a currentsource 422, a transistor M1, a transistor M1 b, a transistor M2 and atransistor M2 b. In the present embodiment, the transistor M1 and thetransistor M1 b are PMOS transistors, and the transistor M2 and thetransistor M2 b are NMOS transistors.

A first end of the current source 421 is connected to a first end (forexample, a source) of the transistor M1, and a second end of the currentsource 421 is connected to a first reference voltage (for example, thepower voltage VDD). The first end of the transistor M1 is furtherconnected to the first input terminal of the input stage 420, so thatthe first end of the transistor M1 may receive a current I_(ss1) of thecurrent source 421 and the first input current I_(in+) of the inputstage 420. A first end of the current source 422 is connected to a firstend (for example, a source) of the transistor M1 b, and a second end ofthe current source 422 is connected to the first reference voltage. Thefirst end of the transistor M1 b is further connected to the secondinput terminal of the input stage 420, so that the first end of thetransistor M1 b may receive the current I_(ss2) of the current source422 and the second input current I_(in−) of the input stage 420.

Control ends (for example, gates) of the transistor M1 and thetransistor M1 b are controlled by the feedback circuit 410. A second end(for example, a drain) of the transistor M1 is connected to a first end(for example, a drain) of the transistor M2. A control end (for example,a gate) of the transistor M2 is connected to the first end of thetransistor M2. A common node of the transistor M2 and the transistor M1is connected to the first output terminal of the input stage 420 forproviding a first inner signal 401 to the output stage 430. A second end(for example, a drain) of the transistor M1 b is connected to a firstend (for example, a drain) of the transistor M2 b. A control end (forexample, a gate) of the transistor M2 b is connected to the first end ofthe transistor M2 b. A common node of the transistor M2 b and thetransistor M1 b is connected to the second output terminal of the inputstage 420 for providing a second inner signal 402 to the output stage430. Second ends (for example, sources) of the transistor M2 and thetransistor M2 b are connected to a second reference voltage (forexample, the ground voltage).

The feedback circuit 410 includes impedances 411 and 412, a transistorM3 and a transistor M3 b. The impedance 411 and the impedance 412 can beimpedance devices such as resistors, transistors, or diodes, etc. In thepresent exemplary embodiment, the impedance 411 includes a transistorM4, and the impedance 412 includes a transistor M4 b. In the presentexemplary embodiment, the transistor M3, the transistor M3B, thetransistor M4 and the transistor M4 b are NMOS transistors.

A first end (for example, a drain) of the transistor M4 is connected tothe first reference voltage, and a second end (for example, a source) ofthe transistor M4 is connected to the control end of the transistor M1.A first end (for example, a drain) of the transistor M3 is connected tothe second end of the transistor M4, a second end (for example, asource) of the transistor M3 is connected to the second referencevoltage, and a control end (for example, a gate) of the transistor M3 isconnected to the first end of the transistor M2. The transistor M2 andthe transistor M3 form a current mirror, so that the feedback circuit410 can generate the corresponding feedback current I_(fb+) according tothe inner current I_(inner+) of the input stage 420. The transistor M4may convert the feedback current I_(fb+) into a corresponding controlvoltage to control the transistor M1, so as to reduce the inputimpedance of the input stage 420 and achieve the purpose of broadband.By adjusting a bias VB_(n1), a gain of the feedback current I_(fb+) canbe changed. In the present exemplary embodiment, a relationship of theinner current I_(inner+), the input current I_(in+) and the feedbackcurrent I_(fb+) is I_(inner+)=I_(in+)+I_(fb+).

A first end (for example, a drain) of the transistor M4 b is connectedto the first reference voltage, and a second end (for example, a source)of the transistor M4 b is connected to the control end of the transistorM1 b. A first end (for example, a drain) of the transistor M3 b isconnected to the second end of the transistor M4 b, a second end (forexample, a source) of the transistor M3 b is connected to the secondreference voltage, and a control end (for example, a gate) of thetransistor M4 b is connected to the first end of the transistor M2 b.The transistor M2 b and the transistor M3 b form a current mirror, sothat the feedback circuit 410 can generate a corresponding feedbackcurrent I_(fb−) according to the inner current I_(inner−) of the inputstage 420. The transistor M4 b may convert the feedback current into acorresponding control voltage to control the transistor M1 b, so as toreduce the input impedance of the input stage 420 and achieve thepurpose of broadband. By adjusting the bias VB_(n1), a gain of thefeedback current I_(fb−) can be changed. In the present exemplaryembodiment, a relationship of the inner current I_(inner−), the inputcurrent I_(in−) and the feedback current I_(fb−) isI_(inner−)=I_(in−)+I_(fb−).

The output stage 430 includes a transistor M9, a transistor M10, atransistor M11, a transistor M12, a transistor M13 and a transistor M14.In the present exemplary embodiment, the transistors M9 and M10 are PMOStransistors, and the transistors M11, M12, M13 and M14 are NMOStransistors. A first end (for example, a drain) of the transistor M9 isconnected to the first output terminal of the output stage 430. A firstend (for example, a drain) of the transistor M10 is connected to thesecond output terminal of the output stage 430. Control ends (forexample, gates) of the transistors M9 and M10 receive a first biasVB_(p2). Second ends (for example, sources) of the transistors M9 andM10 are connected to the first reference voltage (for example, the powervoltage VDD).

A first end (for example, a drain) of the transistor M13 is connected tothe first end of the transistor M9, and a second end (for example, asource) of the transistor M13 is connected to a first end (for example,a drain) of the transistor M11. A first end (for example, a drain) ofthe transistor M14 is connected to the first end of the transistor M10,and a second end (for example, a source) of the transistor M14 isconnected to a first end of the transistor M12. Control ends (forexample, gates) of the transistors M13 and M14 receive a bias VB_(n2). Acontrol end (for example, a gate) of the transistor M11 is connected tothe first input terminal of the output stage 430 for receiving the firstinner signal 401. A control end (for example, a gate) of the transistorM12 is connected to the second input terminal of the output stage 430for receiving the second inner signal 402. Second ends (for example,sources) of the transistors M11 and M12 are connected to the secondreference voltage (for example, the ground voltage).

The transistors M2, M2 b, M3, M3 b, M11 and M12 form the current mirrorstructure 405. The transistors M2 and M11 form a current minor, whereinchannel aspect ratios (or channel width/length ratios W/L) of thetransistors M2 and M11 are 1:F. According to the first inner signal 401,the output stage 430 can mirror the inner current I_(inner+) of theinput stage 420 to internal of the output stage 430 by a multiplicationfactor of F. Similarly, the transistors M2 b and M12 form anothercurrent minor, wherein channel aspect ratios (or channel width/lengthratios W/L) of the transistors M2 b and M12 are 1:F. According to thesecond inner signal 402, the output stage 430 can mirror the innercurrent I_(inner−) of the input stage 420 to internal of the outputstage 430 by a multiplication factor of F. By determining theproportional relation of 1:F, a current gain of the output stage 430 canbe set. Now, the output stage 430 outputs a first output current signalI_(out+) and a second output current signal I_(out−) according to theinner currents I_(inner+) and I_(inner−) with reference of the abovecurrent gain. After the resistors R₁, R₂, R₃ and R₄, and the capacitorsC₁, C₂, C₃ and C₄ filter the current signals I_(out+) and I_(out−),signals I₁₊ and I¹⁻ (i.e. the signal I₁ of FIG. 1) are output to thefirst current-mode PGA unit 120.

In summary, based on a local feedback mode of the feedback circuit 410,a low impedance input stage is implemented by the transistors M1, M2, M1b and M2 b. The inner currents I_(inner+) and I_(inner−) of the inputstage 420 are respectively transmitted (mirrored) to the output stage430 by a predetermined multiplication factor by using the current mirrorstructure 405. An input impedance Z_(in) of the current-mode amplifier400 of FIG. 4 in an s-domain can be represented by a following equation(1):

$\begin{matrix}{Z_{in} = {\frac{1}{g_{m\; 1}} \cdot \frac{{s^{2}C_{A}C_{B}} + {S\left( {{C_{A}g_{m\; 2}} + {C_{B}g_{m\; 4}}} \right)} + \left( {{g_{m\; 4}g_{m\; 2}} - {g_{m\; 1}g_{m\; 3}}} \right)}{\begin{matrix}{{s^{3}\frac{C_{A}C_{B}C_{in}}{g_{m\; 1}}} + {s^{2}\left\lbrack {{C_{A}C_{B}} + {\frac{C_{in}}{g_{m\; 1}}\left( {{C_{A}g_{m\; 2}} + {C_{B}g_{m\; 4}}} \right)}} \right\rbrack} +} \\{{s\left\lbrack {{C_{A}g_{m\; 2}} + {C_{B}g_{m\; 4}} + {\frac{C_{in}}{g_{m\; 1}}\left( {{g_{m\; 4}g_{m\; 2}} - {g_{m\; 1}g_{m\; 3}}} \right)}} \right\rbrack} + {g_{m\; 4}g_{m\; 2}}}\end{matrix}}}} & {{equation}\mspace{14mu} (1)}\end{matrix}$

Wherein, g_(m1), g_(m2), g_(m3) and g_(m4) respectively representconductances of the transistors M1, M2, M3 and M4. C_(in) represents aparasitic capacitance of the first input terminal of the input stage420. A parasitic capacitance C_(A)=C_(gs4) C_(ds4) C_(ds3), whereinC_(gs4) represents a parasitic capacitance from the gate to the sourceof the transistor M4, C_(ds4) represents a parasitic capacitance fromthe drain to the source of the transistor M4, and C_(ds3) represents aparasitic capacitance from the drain to the source of the transistor M3.A parasitic capacitance C_(B)=C_(gs2) C_(ds2) C_(gs3), wherein C_(gs2)represents a parasitic capacitance from the gate to the source of thetransistor M2, C_(ds2) represents a parasitic capacitance from the drainto the source of the transistor M2, and C_(gs3) represents a parasiticcapacitance from the gate to the source of the transistor M3. In case ofa low frequency, the equation (1) can be simplified as:

$\begin{matrix}{Z_{{in},{DC}} = {\frac{1}{g_{m\; 1}} \cdot \left( {1 - {\frac{g_{m\; 1}}{g_{m\; 4}} \cdot \frac{g_{m\; 3}}{g_{m\; 2}}}} \right)}} & {{equation}\mspace{14mu} (2)}\end{matrix}$

Therefore, the input impedance can be reduced through the feedbackcircuit 410, so as to achieve the purpose of broadband.

In other exemplary embodiments, the transistors M13 and M14 can beomitted, so that the first end of the transistor M11 and the first endof the transistor M12 are respectively connected to the first end of thetransistor M9 and the first end of the transistor M10, directly.Moreover, in other exemplary embodiments, the transistors M1, M1 b, M9and M10 show in FIG. 4 can be NMOS transistors, and the othertransistors can be PMOS transistors. The drains of the transistor M4 andM4 b, the sources of the transistors M9 and M10, and the current sources421 and 422 can be connected to the ground voltage. The sources of thetransistors M3, M3 b, M2, M2 b, M11 and M12 can be connected to thepower voltage VDD.

FIG. 5 is a diagram illustrating an implementation of the firstcurrent-mode PGA unit 120 of FIG. 1. In FIG. 5, a single current-modeamplifier is used to implement the first current-mode PGA unit 120. Inother exemplary embodiments, the first current-mode PGA unit 120 can beimplemented by a plurality of current-mode amplifiers mutually connectedin series.

As shown in FIG. 5, the first current-mode PGA unit 120 includes afeedback circuit 510, an input stage 520 and an output stage 530. Theinput stage 520 has an input terminal for receiving an input current(the output signal I₁ of the current-mode low-order filter 110). Theinput stage 520 generates a corresponding inner current according to thesignal I₁ and a feedback current of the feedback circuit 510. The inputstage 520 may use a common source complementary metal-oxidesemiconductor (CMOS) amplifier in collaboration with the feedbackcircuit 510 to achieve an effect of reducing the input impedance. Inother exemplary embodiments, the input stage 520 may use a common basebipolar junction transistor (BJT) amplifier in collaboration with thefeedback circuit 510 to achieve the effect of reducing the inputimpedance.

The feedback circuit 510 is connected to the input stage 520. Thefeedback circuit 510 generates the corresponding feedback currentaccording to the inner current of the input stage 520. In some exemplaryembodiments, the feedback circuit 510 can be a trans-impedance amplifier(TIA). A relationship of the inner current, the input current I₁ and thefeedback current is determined according to a design requirement. Forexample, the inner current is a sum of the input current I₁ and thefeedback current. The feedback circuit 510 may reduce the inputimpedance of the input stage 520, so as to achieve a purpose ofbroadband.

An input terminal of the output stage 530 is connected to an outputterminal of the input stage 520. An output terminal of the output stage530 serves as an output terminal of the current-mode amplifier. Theoutput stage 530 generates a corresponding output current (the outputsignal I₂) according to the inner current of the input stage 520. Theoutput stage 530 has one or a plurality of gain circuits, for example, Kgain circuits 530-1, 530-2, . . . , 530-K shown in FIG. 5. According toa gain requirement, by controlling a bias voltage of each of the gaincircuits 530-1˜530-K, a part of the gain circuits is enabled, and theother gain circuits are disabled. By enabling and disabling the gaincircuits 530-1˜530-K, a gain of the current-mode amplifier is adjusted,so as to achieve a variable gain effect.

FIG. 6 is a circuit schematic diagram of the current-mode amplifier ofFIG. 5 according to an exemplary embodiment of the disclosure. In thepresent exemplary embodiment, the input current I₁ includes a firstinput current I₁₊ and a second input current I¹⁻, and the output currentI₂ includes a first output current I₂₊ and a second output current I²⁻.In FIG. 6, two gain circuits 530-1 and 530-2 connected in parallel areused to implement the output stage 530, though a number of the gaincircuits can be determined according to an actual design requirement.For example, the gain circuit 530-2 can be omitted, or more gain circuit530-2 can be applied.

The input terminal of the input stage 520 includes a first inputterminal used for receiving the first input current I₁₊ and a secondinput terminal used for receiving the second input current I²⁻. Theoutput terminal of the input stage 520 include a first output terminalused for providing a first inner signal 601 and a second output terminalused for providing a second inner signal 602. Based on a current mirrorstructure 610, the input stage 520 may convert a first inner currentI′_(inner+) and a second inner current I′_(inner−) into thecorresponding first inner signal 601 and the second inner signal 602.The output stage 530 can mirror the inner currents I′_(inner+) andI′_(inner−) of the input stage 520 to internal of the output stage 530according to the first inner signal 601 and the second inner signal 602.

The input stage 520 includes a first current source 521, a secondcurrent source 522, a transistor Q1, a transistor Q1 b, a transistor Q2and a transistor Q2 b. In the present exemplary embodiment, thetransistors Q1 and Q1 b are PMOS transistors, and the transistors Q2 andQ2 b are NMOS transistors. A first end of the current source 521 isconnected to a first end (for example, a source) of the transistor Q1, asecond end of the current source 521 is connected to the first referencevoltage (for example, the power voltage VDD). The first end of thetransistor Q1 is further connected to the first input terminal of theinput stage 520, so that the first end of the transistor Q1 may receivea current Iss of the current source 521 and the first input current I₁₊of the input stage 520. A first end of the current source 522 isconnected to a first end (for example, a source) of the transistor Q1 b,and a second end of the current source 522 is connected to the firstreference voltage. The first end of the transistor Q1 b is furtherconnected to the second input terminal of the input stage 520, so thatthe first end of the transistor Q1 b may receive the current Iss of thecurrent source 522 and the second input current I¹⁻ of the input stage520.

Control ends (for example, gates) of the transistor Q1 and thetransistor Q1 b are controlled by the feedback circuit 510. A second end(for example, a drain) of the transistor Q1 is connected to a first end(for example, a drain) of the transistor Q2. A control end (for example,a gate) of the transistor Q2 is connected to the first end of thetransistor Q2. A common node of the transistor Q2 and the transistor Q1is connected to the first output terminal of the input stage 520 forproviding the first inner signal 601. A second end (for example, adrain) of the transistor Q1 b is connected to a first end (for example,a drain) of the transistor Q2 b. A control end (for example, a gate) ofthe transistor Q2 b is connected to the first end of the transistor Q2b. A common node of the transistor Q2 b and the transistor Q1 b isconnected to the second output terminal of the input stage 520 forproviding the second inner signal 502. Second ends (for example,sources) of the transistor Q2 and the transistor Q2 b are connected tothe second reference voltage (for example, the ground voltage).

The feedback circuit 510 includes a first impedance 511, a secondimpedance 512, a transistor Q3 and a transistor Q3 b. The firstimpedance 511 and the second impedance 512 can be impedance devices suchas resistors, transistors, or diodes, etc. In the present exemplaryembodiment, the first impedance 511 includes a transistor Q4, and thesecond impedance 512 includes a transistor Q4 b. In the presentexemplary embodiment, the transistor Q3, the transistor Q3B, thetransistor Q4 and the transistor Q4 b are NMOS transistors.

A first end (for example, a drain) of the transistor Q4 is connected tothe first reference voltage, and a second end (for example, a source) ofthe transistor Q4 is connected to the control end of the transistor Q1.A first end (for example, a drain) of the transistor Q3 is connected tothe second end of the transistor Q4, a second end (for example, asource) of the transistor Q3 is connected to the second referencevoltage, and a control end (for example, a gate) of the transistor Q3 isconnected to the first end of the transistor Q2. The transistor Q2 andthe transistor Q3 form a current mirror, so that the feedback circuit510 can generate a corresponding feedback current I′_(fb+) according tothe inner current I′_(inner+) of the input stage 520. The transistor Q4may convert the feedback current I′_(fb+) into a corresponding controlvoltage to control the transistor Q1, so as to reduce the inputimpedance of the input stage 520 and achieve the purpose of broadband.By adjusting the bias VB_(n1), a gain of the feedback current I′_(fb+)can be changed. In the present exemplary embodiment, a relationship ofthe inner current I′_(inner+), the input current I₁₊ and the feedbackcurrent I′_(fb+) is F_(inner+)=I₁₊+I′_(fb+).

A first end (for example, a drain) of the transistor Q4 b is connectedto the first reference voltage, and a second end (for example, a source)of the transistor Q4 b is connected to the control end of the transistorQ1 b. A first end (for example, a drain) of the transistor Q3 b isconnected to the second end of the transistor Q4 b, a second end (forexample, a source) of the transistor Q3 b is connected to the secondreference voltage, and a control end (for example, a gate) of thetransistor Q3 b is connected to the first end of the transistor Q2 b.The transistor Q2 b and the transistor Q3 b form a current mirror, sothat the feedback circuit 510 can generate a corresponding feedbackcurrent I′_(fb−) according to the inner current I′_(inner−) of the inputstage 520. The transistor Q4 b may convert the feedback current I′_(fb−)into a corresponding control voltage to control the transistor Q1 b, soas to reduce the input impedance of the input stage 520 and achieve thepurpose of broadband. By adjusting the bias VB_(n1), a gain of thefeedback current I′_(fb−) can be changed. In the present exemplaryembodiment, a relationship of the inner current I′_(inner−), the inputcurrent I¹⁻ and the feedback current I′_(fb−) isI′_(inner−)=I¹⁻+I′_(fb−).

The input terminal of the output stage 530 includes a first inputterminal used for receiving the first inner signal 601 and a secondinput terminal used for receiving the second inner signal 602, and theoutput terminal of the output stage 530 includes a first output terminalused for providing the first output current I₂₊ and a second outputterminal used for providing the second output current I²⁻. The gaincircuit 530-1 of the output stage 530 includes a transistor Q9, atransistor Q10, a transistor Q11, a transistor Q12, a transistor Q13 anda transistor Q14. In the present exemplary embodiment, the transistorsQ9 and Q10 are PMOS transistors, and the transistors Q11, Q12, Q13 andQ14 are NMOS transistors. A first end (for example, a drain) of thetransistor Q9 is connected to the first output terminal of the outputstage 530 and a first end (for example, a drain) of the transistor Q13.A control end (for example, a gate) of the transistor Q9 receives afirst bias VB. A first end (for example, a drain) of the transistor Q10is connected to the second output terminal of the output stage 530 and afirst end (for example, a drain) of the transistor Q14. Second ends (forexample, sources) of the transistors Q9 and Q10 are connected to thefirst reference voltage (for example, the power voltage VDD). A controlend (for example, a gate) of the transistor Q10 receives the first biasVB. The first bias VB can be a band-gap reference voltage or acommon-mode feedback (CMFB) voltage or other fixed voltages.

Control ends (for example, gates) of the transistors Q13 and Q14 receivethe second bias VB_(n2). The second bias VB_(n2) can be a band-gapreference voltage or other fixed voltages. A second end (for example, asource) of the transistor Q13 is connected to a first end (for example,a drain) of the transistor Q11. A second end (for example, a source) ofthe transistor Q14 is connected to a first end (for example, a drain) ofthe transistor Q12. A control end (for example, a gate) of thetransistor Q11 is connected to the first input terminal of the outputstage 530 for receiving the first inner signal 601. A control end (forexample, a gate) of the transistor Q12 is connected to the second inputterminal of the output stage 530 for receiving the second inner signal602. Second ends (for example, sources) of the transistors Q11 and Q12are connected to the second reference voltage (for example, the groundvoltage).

The gain circuit 530-2 of the output stage 530 includes a first switchSWp, a second switch SWn, a transistor Q15, a transistor Q16, atransistor Q17, a transistor Q18, a transistor Q19 and a transistor Q20.In the present exemplary embodiment, the transistors Q15 and Q16 arePMOS transistors, and the transistors Q17, Q18, Q19 and Q20 are NMOStransistors. A first end (for example, a drain) of the transistor Q15 isconnected to the first output terminal of the output stage 530 and afirst end (for example, a drain) of the transistor Q19. A first end (forexample, a drain) of the transistor M16 is connected to the secondoutput terminal of the output stage 530 and a first end (for example, adrain) of the transistor Q20. Second ends (for example, sources) of thetransistors Q15 and Q16 are connected to the first reference voltage(for example, the power voltage VDD). The first bias VB or the firstreference voltage (for example, the power voltage VDD) is selected andtransmitted to control ends (for example, gates) of the transistors Q15and Q16 through the first switch SWp.

A second end (for example, a source) of the transistor Q19 is connectedto a first end (for example, a drain) of the transistor Q17. A secondend (for example, a source) of the transistor Q20 is connected to afirst end (for example, a drain) of the transistor Q18. The second biasVB_(n2) or the second reference voltage (for example, the groundvoltage) is selected and transmitted to control ends (for example,gates) of the transistors Q19 and Q20 through the second switch SWn. Acontrol end (for example, a gate) of the transistor Q17 is connected tothe first input terminal of the output stage 530 for receiving the firstinner signal 601. A control end (for example, a gate) of the transistorQ18 is connected to the second input terminal of the output stage 530for receiving the second inner signal 602. Second ends (for example,sources) of the transistors Q17 and Q18 are connected to the secondreference voltage (for example, the ground voltage).

When the first bias VB is selected and transmitted to the control endsof the transistors Q15 and Q16 through the first switch SWp, and thesecond bias VB_(n2) is selected and transmitted to the control ends ofthe transistors Q19 and Q20 through the second switch SWn, a circuitstructure of the gain circuit 530-2 is similar to that of the gaincircuit 530-1. The transistors Q2, Q2 b, Q11, Q12, Q17 and Q18 form thecurrent mirror structure 610. The transistors Q2, Q11 and Q17 form acurrent mirror, wherein channel aspect ratios (or channel width/lengthratios W/L) of the transistors Q2, Q11 and Q17 are 1:M:N. According tothe first inner signal 601, the gain circuits 530-1 and the 530-2 canrespectively mirror the inner current I′_(inner+) of the input stage 520to internals of the gain circuits 530-1 and 530-2 by multiplicationfactors of M and N. The transistors Q2 b, Q12 and Q18 form anothercurrent mirror, wherein channel aspect ratios (or channel width/lengthratios W/L) of the transistors Q2 b, Q12 and Q18 are 1:M:N. According tothe second inner signal 602, the gain circuits 530-1 and the 530-2 canrespectively mirror the inner current I′_(inner−) to internals of thegain circuits 530-1 and 530-2 by multiplication factors of M and N. Bydetermining the proportional relation of 1:M:N, current gains of thegain circuits 530-1 and 530-2 can be set. Now, the gain circuits 530-1and 530-2 commonly provide the first output current I₂+ and the secondoutput current I²⁻, namely, the current-mode amplifier has a relativelygreat output gain.

When the power voltage VDD is selected and transmitted to the controlends of the transistors Q15 and Q16 through the first switch SWp, andthe ground voltage is selected and transmitted to the control ends ofthe transistors Q19 and Q20 through the second switch SWn, thetransistors Q15, Q16, Q19 and Q20 are turned off, which is equivalent toa situation that the gain circuit 530-2 is disabled. By turning off thetransistors Q15, Q16, Q19 and Q20, it can be ensured that the disabledgain circuit 530-2 does not influence the output currents I₂₊ and I²⁻ ofthe output stage 530. Now, the first output current I₂₊ and the secondoutput current I²⁻ are provided by the gain circuit 530-1 alone, namely,the current-mode amplifier has a relatively small output gain.Therefore, by controlling the first switch SWp and the second switchSWn, the gain of the current-mode amplifier can be changed, so as toachieve an effect of a variable gain amplifier (VGA).

In other exemplary embodiments, the second switch SWn, the transistorsQ13, Q14, Q19 and Q20 can be omitted, so that the drains of thetransistors Q11, Q12, Q17 and Q18 can be respectively connected to thedrains of the transistors Q9, Q10, Q15 and Q16, directly. Moreover, inother exemplary embodiments, the transistors Q1, Q1 b, Q9, Q10, Q15 andQ16 of FIG. 6 can be NMOS transistors, and the other transistors thereofcan be PMOS transistors. The drains of the transistors Q4 and Q4 b, thesources of the transistors Q9, Q10, Q15 and Q16, and the current sources521 and 522 can be connected to the ground voltage, and the sources ofthe transistors Q3, Q3 b, Q2, Q2 b, Q11, Q12, Q17 and Q18 can beconnected to the power voltage VDD.

The analog baseband apparatus 100 of FIG. 1 can used to implement ananalog baseband structure of a UWB wireless transceiver system, as thatshown in FIG. 7. FIG. 7 is a functional block schematic diagram of ananalog baseband apparatus 700 according to another exemplary embodimentof the disclosure. The analog baseband apparatus 700 can be widelyapplied to various wireless/cable broadband systems, and can be used toimplement an analog baseband circuit in the broadband system foradjusting a magnitude of a received signal and filter interferencesignals outside the channels.

The analog baseband apparatus 700 has an in-phase component signal pathand a quadrature-phase component signal path. The in-phase componentsignal path includes the current-mode low-order filter 110, the firstcurrent-mode PGA unit 120, the high-order filter 130, a current-modesecond PGA unit 740, a current-to-voltage converter 760 and a buffer780. The in-phase component signal path directly demultiplies acurrent-mode RF signal pair I_(in+) ^(I) and I_(in−) ^(I) to avoltage-mode baseband signal pair V_(out+) ^(I) and V_(out−) ^(I).

The current-mode low-order filter 110 receives the current-mode RFsignal pair I_(in+) ^(I) and I_(in−) ^(I). Implementations of thecurrent-mode low-order filter 110, the first current-mode PGA unit 120,and the high-order filter 130 of FIG. 7 are as that described in theexemplary embodiment of FIG. 1, so that detailed descriptions thereofare not repeated. An input terminal of the second current-mode PGA unit740 is connected to the output terminal of the high-order filter 130. Acurrent input terminal of the current-to-voltage converter 760 isconnected to an output terminal of the second current-mode PGA unit 740.An input terminal of the buffer 780 is connected to a voltage outputterminal of the current-to-voltage converter 760. The voltage outputterminal of the current-to-voltage converter 760 provides thevoltage-mode baseband signal pair V_(out+) ^(I) and V_(out−) ^(I).

The first current-mode PGA unit 120 and the second current-mode PGA unit740 can be respectively implemented by one or a plurality ofcurrent-mode programmable gain amplifiers (PGAs). The current-mode PGAscan be current-mode amplifiers of any type, for example, thecurrent-mode amplifiers shown in FIG. 3B and FIG. 5 or other types ofthe current amplifiers, etc. Implementation of the first current-modePGA unit 120 can be the same to that of the second current-mode PGA unit740. In other exemplary embodiments, implementation of the firstcurrent-mode PGA unit 120 can be different to that of the secondcurrent-mode PGA unit 740. Moreover, implementation of thecurrent-to-voltage converter 760 is not limited by the disclosure, andany circuit/device capable of converting a current-mode signal into avoltage-mode signal can be used to implement the current-to-voltageconverter 760. For example, a current-mode signal may flow through aresistor, and the resistor can be used to convert the current-modesignal into a voltage-mode signal.

The quadrature-phase component signal path includes a secondcurrent-mode low-order filter 710, a third current-mode PGA unit 720, asecond high-order filter 730, a fourth current-mode PGA unit 750, asecond current-to-voltage converter 770 and a second buffer 790. Thequadrature-phase component signal path directly demultiplies acurrent-mode RF signal pair I_(in+) ^(Q) and I_(in−) ^(Q) to avoltage-mode baseband signal pair V_(out−) ^(Q) and I_(out−) ^(Q).Implementations of the second current-mode low-order filter 710, thethird current-mode PGA unit 720, the second high-order filter 730, thefourth current-mode PGA unit 750, the second current-to-voltageconverter 770 and the second buffer 790 are the same as that of thecurrent-mode low-order filter 110, the first current-mode PGA unit 120,the high-order filter 130, the second current-mode PGA unit 740, thecurrent-to-voltage converter 760 and the buffer 780.

The current-mode low-order filters 110 and 710 first provide apreliminary filtering of the interference signals outside the channels,so as to relax a linearity requirement of the post-stage current-modePGA units 120 and 720. High-order filtering of the interference signalsoutside the channels is performed through the high-order filters 130 and730 in the analog baseband apparatus 700. Based on such configuration,noise and linearity characteristic performance of the whole analogbaseband apparatus 700 are simultaneously taken into consideration, soas to achieve an optimal signal-to-noise ratio characteristic.

It is assumed that the current-mode low-order filters 110 and 710 of theanalog baseband apparatus 700 are current-mode Sallen-Key (SK) low-passfilters, and the high-order filters 130 and 730 are gm-C low-passfilters. FIG. 8 is a diagram illustrating a simulation result of theinput impedance of the analog baseband apparatus 700 of FIG. 7. In FIG.8, a vertical axis represents the input impedances, and a horizontalaxis represents frequencies. According to FIG. 8, it is known that thebandwidth of the analog baseband apparatus 700 may reach 1 GHz.

FIG. 9 is a gain frequency response diagram of the current-mode PGA (forexample, the current-mode amplifiers of FIG. 5 and FIG. 6) of thecurrent-mode PGA unit in the analog baseband apparatus 700 of FIG. 7. InFIG. 9, a vertical axis represents gains, and a horizontal axisrepresents frequencies. According to FIG. 9, it is known that underdifferent gain modulations, the current-mode amplifier may stillmaintain the bandwidth of 1 GHz.

FIG. 10 is a diagram illustrating a frequency response simulation resultof the current-mode low-order filter 110 in the analog basebandapparatus 700 of FIG. 7. Here, the current-mode low-order filter 110 isa current-mode SK low-pass filter. In FIG. 10, a vertical axisrepresents gains, and a horizontal axis represents frequencies.According to FIG. 10, it is known that the current-mode low-order filter110 may preliminarily filter the interference signals outside thechannels.

FIG. 11 is a diagram illustrating a whole frequency response simulationand measurement result of the analog baseband apparatus 700 of FIG. 7.In FIG. 11, a vertical axis represents signal magnitudes, and ahorizontal axis represents frequencies. Wherein, a curve 1103 is a wholesimulation frequency response curve of the analog baseband apparatus 700in case that the current-mode low-order filters 110 and 710 are omitted,and the gm-C low-pass filters are used to implement the high-orderfilters 130 and 730. A curve 1102 is a whole simulation frequencyresponse curve of the analog baseband apparatus 700 in case that thecurrent-mode SK low-pass filters are used to implement the current-modelow-order filters 110 and 710, and the gm-C low-pass filters are used toimplement the high-order filters 130 and 730. A curve 1101 is an actualmeasurement frequency response curve of the analog baseband apparatus700 in case of a same condition of the curve 1102. According to FIG. 11,it is known that the analog baseband apparatus 700 performs thehigh-order filtering to the interference signals outside the channels.

FIG. 12 is a diagram illustrating a whole noise characteristicmeasurement result of the analog baseband apparatus 700 of FIG. 7. InFIG. 12, a vertical axis represents a noise figure, and a horizontalaxis represents frequencies. According to FIG. 12, it is known that theanalog baseband apparatus 700 has a low noise characteristic.

In summary, signals within 250 MHz are amplified according to abroadband feature of the current-mode amplifiers of the above exemplaryembodiments, so as to overcome a technical difficulty that thevoltage-mode amplifier cannot be operated over 100 MHz. Moreover, a gaincontrol of the current-mode amplifier of the exemplary embodiments isachieved by controlling a current mirror, so that a problem of a gainerror influenced by a fabrication variation can be resolved. The analogbaseband apparatus of the disclosure is used to amplify the signalreceived by a receiver to a full-scale of an analog-to-digitalconverter, so as to reduce a demand for a dynamic range of theanalog-to-digital converter, and filter the interference signals outsidethe channels. The analog baseband apparatus of the disclosure is adaptedto be implemented by a circuit with a low operation voltage.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of thedisclosure without departing from the scope or spirit of the disclosure.In view of the foregoing, it is intended that the disclosure covermodifications and variations of this disclosure provided they fallwithin the scope of the following claims and their equivalents.

1. An analog baseband apparatus, comprising: a current-mode low-orderfilter, wherein an input impedance of the current-mode low-order filteris smaller than an output impedance thereof; a first current-modeprogrammable gain amplifier (PGA) unit, having an input terminalconnected to an output terminal of the current-mode low-order filter;and a high-order filter, having an input terminal connected to an outputterminal of the first current-mode PGA unit.
 2. The analog basebandapparatus as claimed in claim 1, wherein the current-mode low-orderfilter is a current-mode low-pass filter.
 3. The analog basebandapparatus as claimed in claim 2, wherein the current-mode low-orderfilter is a current-mode Sallen-Key filter.
 4. The analog basebandapparatus as claimed in claim 1, wherein the current-mode low-orderfilter comprises: a current-mode amplifier, having an input terminalserving as an input terminal of the current-mode low-order filter; afeedback capacitor, having a first end connected to the input terminalof the current-mode amplifier; an output capacitor, having a first endconnected to an output terminal of the current-mode amplifier; a firstresistor, having a first end connected to the output terminal of thecurrent-mode amplifier, and a second end connected to a second end ofthe feedback capacitor; and a second resistor, having a first endconnected to the second end of the first resistor, and a second endserving as the output terminal of the current-mode low-order filter. 5.The analog baseband apparatus as claimed in claim 1, wherein thecurrent-mode low-order filter comprises: a current-mode amplifier,having a first input terminal and a second input terminal serving asinput terminals of the current-mode low-order filter; a first feedbackcapacitor, having a first end connected to the first input terminal ofthe current-mode amplifier; a second feedback capacitor, having a firstend connected to the second input terminal of the current-modeamplifier; a first output capacitor, having a first end connected to afirst output terminal of the current-mode amplifier; a second outputcapacitor, having a first end connected to a second output terminal ofthe current-mode amplifier; a first resistor, having a first endconnected to the first output terminal of the current-mode amplifier,and a second end connected to a second end of the first feedbackcapacitor; a second resistor, having a first end connected to the secondend of the first resistor; a third resistor, having a first endconnected to the second output terminal of the current-mode amplifier,and a second end connected to a second end of the second feedbackcapacitor; and a fourth resistor, having a first end connected to thesecond end of the third resistor, and second ends of the second resistorand the fourth resistor serve as the output terminal of the current-modelow-order filter.
 6. The analog baseband apparatus as claimed in claim5, wherein the current-mode amplifier comprises: an input stage, havinga first input terminal and a second input terminal respectively servingas the first input terminal and the second input terminal of thecurrent-mode amplifier for receiving an input current, wherein the inputstage generates an inner current according to the input current and afeedback current; an output stage, having a first input terminal and asecond input terminal connected to the a first output terminal and asecond output terminal of the input stage, and a first output terminaland a second output terminal respectively serving as the first outputterminal and the second output terminal of the current-mode amplifier;and a feedback circuit, connected to the input stage, for generating thefeedback current according to the inner current of the input stage. 7.The analog baseband apparatus as claimed in claim 6, wherein the innercurrent is a sum of the input current and the feedback current.
 8. Theanalog baseband apparatus as claimed in claim 6, wherein the input stagecomprises: a first current source; a second current source; a firsttransistor, having a first end connected to a first end of the firstcurrent source, and a control end controlled by the feedback circuit,wherein a common node of the first transistor and the first currentsource is connected to the first input terminal of the input stage; asecond transistor, having a first end connected to a first end of thesecond current source, and a control end controlled by the feedbackcircuit, wherein a common node of the second transistor and the secondcurrent source is connected to the second input terminal of the inputstage; a third transistor, having a first end connected to a second endof the first transistor, and a control end connected to the first end ofthe third transistor, wherein a common node of the third transistor andthe first transistor is connected to the first output terminal of theinput stage; and a fourth transistor, having a first end connected to asecond end of the second transistor, and a control end connected to thefirst end of the fourth transistor, wherein a common node of the fourthtransistor and the second transistor is connected to the second outputterminal of the input stage.
 9. The analog baseband apparatus as claimedin claim 8, wherein the feedback circuit comprises: a first impedance,having a first end connected to a first reference voltage, and a secondend connected to the control end of the first transistor; a secondimpedance, having a first end connected to the first reference voltage,and a second end connected to the control end of the second transistor;a fifth transistor, having a first end connected to the second end ofthe first impedance, a second end connected to a second referencevoltage, and a control end connected to the first end of the thirdtransistor; and a sixth transistor, having a first end connected to thesecond end of the second impedance, a second end connected to the secondreference voltage, and a control end connected to the first end of thefourth transistor.
 10. The analog baseband apparatus as claimed in claim9, wherein the first impedance comprises a seventh transistor, and thesecond impedance comprises an eighth transistor.
 11. The analog basebandapparatus as claimed in claim 6, wherein the output stage comprises: aninth transistor, having a first end connected to the first outputterminal of the output stage, and a control end receiving a first bias;a tenth transistor, having a first end connected to the second outputterminal of the output stage, and a control end receiving the firstbias; an eleventh transistor, having a first end connected to the firstend of the ninth transistor, and a control end connected to the firstinput terminal of the output stage; and a twelfth transistor, having afirst end connected to the first end of the tenth transistor, and acontrol end connected to the second input terminal of the output stage.12. The analog baseband apparatus as claimed in claim 6, wherein theoutput stage comprises: a ninth transistor, having a first end connectedto the first output terminal of the output stage, and a control endreceiving a first bias; a tenth transistor, having a first end connectedto the second output terminal of the output stage, and a control endreceiving the first bias; an eleventh transistor, having a control endconnected to the first input terminal of the output stage; a twelfthtransistor, having a control end connected to the second input terminalof the output stage; a thirteenth transistor, having a first endconnected to the first end of the ninth transistor, a second endconnected to a first end of the eleventh transistor, and a control endreceiving a second bias; and a fourteenth transistor, having a first endconnected to the first end of the tenth transistor, a second endconnected to a first end of the twelfth transistor, and a control endreceiving the second bias.
 13. The analog baseband apparatus as claimedin claim 1, wherein the first current-mode PGA unit comprises acurrent-mode amplifier, and the current-mode amplifier comprises: aninput stage, having a first input terminal and a second input terminalrespectively serving as a first input terminal and a second inputterminal of the current-mode amplifier for receiving an input current,wherein the input stage generates an inner current according to theinput current and a feedback current; an output stage, having a firstinput terminal and a second input terminal connected to the a firstoutput terminal and a second output terminal of the input stage, and afirst output terminal and a second output terminal respectively servingas output terminals of the current-mode amplifier; and a feedbackcircuit, connected to the input stage, for generating the feedbackcurrent according to the inner current of the input stage.
 14. Theanalog baseband apparatus as claimed in claim 13, wherein the innercurrent is a sum of the input current and the feedback current.
 15. Theanalog baseband apparatus as claimed in claim 13, wherein the inputstage comprises: a first current source; a second current source; afirst transistor, having a first end connected to a first end of thefirst current source, and a control end controlled by the feedbackcircuit, wherein a common node of the first transistor and the firstcurrent source is connected to the first input terminal of the inputstage; a second transistor, having a first end connected to a first endof the second current source, and a control end controlled by thefeedback circuit, wherein a common node of the second transistor and thesecond current source is connected to the second input terminal of theinput stage; a third transistor, having a first end connected to asecond end of the first transistor, and a control end connected to thefirst end of the third transistor, wherein a common node of the thirdtransistor and the first transistor is connected to the first outputterminal of the input stage; and a fourth transistor, having a first endconnected to a second end of the second transistor, and a control endconnected to the first end of the fourth transistor, wherein a commonnode of the fourth transistor and the second transistor is connected tothe second output terminal of the input stage.
 16. The analog basebandapparatus as claimed in claim 15, wherein the feedback circuitcomprises: a first impedance, having a first end connected to a firstreference voltage, and a second end connected to the control end of thefirst transistor; a second impedance, having a first end connected tothe first reference voltage, and a second end connected to the controlend of the second transistor; a fifth transistor, having a first endconnected to the second end of the first impedance, a second endconnected to a second reference voltage, and a control end connected tothe first end of the third transistor; and a sixth transistor, having afirst end connected to the second end of the second impedance, a secondend connected to the second reference voltage, and a control endconnected to the first end of the fourth transistor.
 17. The analogbaseband apparatus as claimed in claim 16, wherein the first impedancecomprises a seventh transistor, and the second impedance comprises aneighth transistor.
 18. The analog baseband apparatus as claimed in claim13, wherein the output stage comprises: a ninth transistor, having afirst end connected to the first output terminal of the output stage,and a control end receiving a first bias; a tenth transistor, having afirst end connected to the second output terminal of the output stage,and a control end receiving the first bias; an eleventh transistor,having a first end connected to the first end of the ninth transistor,and a control end connected to the first input terminal of the outputstage; a twelfth transistor, having a first end connected to the firstend of the tenth transistor, and a control end connected to the secondinput terminal of the output stage; a fifteenth transistor, having afirst end connected to the first output terminal of the output stage; asixteenth transistor, having a first end connected to the second outputterminal of the output stage; a first switch, selecting to transmit thefirst bias or a first reference voltage to control ends of the fifteenthtransistor and the sixteenth transistor; a seventeenth transistor,having a first end connected to the first end of the fifteenthtransistor, and a control end connected to the first input terminal ofthe output stage; and an eighteenth transistor, having a first endconnected to the first end of the sixteenth transistor, and a controlend connected to the second input terminal of the output stage.
 19. Theanalog baseband apparatus as claimed in claim 13, wherein the outputstage comprises: a ninth transistor, having a first end connected to thefirst output terminal of the output stage, and a control end receiving afirst bias; a tenth transistor, having a first end connected to thesecond output terminal of the output stage, and a control end receivingthe first bias; an eleventh transistor, having a control end connectedto the first input terminal of the output stage; a twelfth transistor,having a control end connected to the second input terminal of theoutput stage; a thirteenth transistor, having a first end connected tothe first end of the ninth transistor, a second end connected to a firstend of the eleventh transistor, and a control end receiving a secondbias; a fourteenth transistor, having a first end connected to the firstend of the tenth transistor, a second end connected to a first end ofthe twelfth transistor, and a control end receiving the second bias; afifteenth transistor, having a first end connected to the first outputterminal of the output stage; a sixteenth transistor, having a first endconnected to the second output terminal of the output stage; a firstswitch, selecting to transmit the first bias or a first referencevoltage to control ends of the fifteenth transistor and the sixteenthtransistor; a seventeenth transistor, having a control end connected tothe first input terminal of the output stage; an eighteenth transistor,having a control end connected to the second input terminal of theoutput stage; a nineteenth transistor, having a first end connected tothe first end of the fifteenth transistor, and a second end connected toa first end of the seventeenth transistor; a twentieth transistor,having a first end connected to the first end of the sixteenthtransistor, and a second end connected to a first end of the eighteenthtransistor; and a second switch, selecting to transmit the second biasor a second reference voltage to control ends of the nineteenthtransistor and the twenties transistor.
 20. The analog basebandapparatus as claimed in claim 1, wherein the high-order filter comprisesa gm-C low-pass filter.
 21. The analog baseband apparatus as claimed inclaim 1, wherein the high-order filter comprises: a current-to-voltageconverter, having a current input terminal connected to the outputterminal of the first current-mode PGA unit; a gm-C low-pass filter,having an input terminal connected to a voltage output terminal of thecurrent-to-voltage converter; and a voltage-to-current converter, havinga voltage input terminal connected to an output terminal of the gm-Clow-pass filter, and a current output terminal connected to an outputterminal of the high-order filter.
 22. The analog baseband apparatus asclaimed in claim 1, wherein the high-order filter is a current-modefilter having current conveyors.
 23. The analog baseband apparatus asclaimed in claim 1, further comprising: a second current-mode PGA unit,having an input terminal connected to an output terminal of thehigh-order filter; and a current-to-voltage converter, having a currentinput terminal connected to an output terminal of the secondcurrent-mode PGA unit.
 24. The analog baseband apparatus as claimed inclaim 23, further comprising: a second current-mode low-order filter,wherein an input impedance of the second current-mode low-order filteris smaller than an output impedance thereof; a third current-mode PGAunit, having an input terminal connected to an output terminal of thesecond current-mode low-order filter; a second high-order filter, havingan input terminal connected to an output terminal of the thirdcurrent-mode PGA unit; a fourth current-mode PGA unit, having an inputterminal connected to an output terminal of the second high-orderfilter; and a second current-to-voltage converter, having a currentinput terminal connected to an output terminal of the fourthcurrent-mode PGA unit.